Positive displacement flush syringe

ABSTRACT

A flush syringe assembly comprises a barrel including a cylindrical side wall having an inside surface defining a chamber for retaining fluid, an open proximal end and a distal end having a passageway therethrough in fluid communication with the chamber. A plunger including an elongate body portion having a stopper at its distal end is provided. The stopper is slidably positioned in fluid-tight engagement with the inside surface of the barrel for driving fluid out of the chamber through the passageway. The stopper includes a distal portion and a proximal portion separated by a spring element and configured to compress when fluid is being driven through the passageway by motion of the plunger and to continue to drive fluid through the passageway after motion of the plunger has stopped.

BACKGROUND OF THE INVENTION

The present invention relates to syringe assemblies and particularly tosyringe assemblies for use in flush procedures, for vascular accessdevices (VAD's).

VAD's are commonly used therapeutic devices. There are two generalclassifications of VAD's, peripheral catheters and central venouscatheters. If not properly maintained, VAD's can become occluded. Toensure VAD's are used properly and do not become occluded, standards ofpractice have been developed. These standards include a cleaningprocedure, which is commonly referred to as a flush procedure orflushing a catheter.

VAD standards of practice usually recommend flush procedures beperformed after catheter placement, before fluid infusion, and beforeand after drug administration, blood sampling, transfusions andparenteral nutrition. The goal of these flush procedures is to confirmcatheter patency, avoid drug incompatibilities, ensure the complete drugdose administration, prevent thrombus formation and minimize the risk ofblood stream infections. Flush procedures require different types andamounts of flush solutions. The most commonly used flush solutions aresaline and or heparin lock solution. The type of flush solution andamount vary depending on the specific type of catheter. Flush solutionvolumes between 5 and 10 ml are most common but can range from 1 to 20ml. Flush procedures also require that care be taken to prevent bloodreflux into the catheter. Reflux in I.V. therapy is the term commonlyused to describe the fluid that is drawn back into the catheter after aflush procedure. The concern is that the reflux fluid contains blood orsolution that could cause the catheter to occlude. To ensure that refluxdoes not occur, flush procedures suggest two techniques: 1) at the endof the flush solution delivery, the user maintains pressure on thesyringe plunger while clamping the I.V. line; or 2) while delivering thelast 0.5 ml of flush solution disconnect the syringe from the I.V.portor clamp the I.V. line. Either technique maintains positive pressure onthe fluid in the VAD to prevent reflux of fluid and blood.

For flush procedures, the I.V. line refers to a system containing a VAD,tubing set with clamp and may terminate with a port or valve. The mostcommon types of I.V. ports are covered by pierceable septums or pre-slitseptums and are known in the art and sometimes referred to as “PRN” fromthe Latin pro re nata meaning “as the need arises”. The septum ispreferably made of rubber or another elastomeric material, which permitsinsertion of a sharp needle cannula in order to infuse fluids or towithdraw fluids from the catheter. Upon withdrawal of the needle cannulathe septum seals itself. Ports having pre-slit septums are used withblunt cannula or the frusto-conically shaped tip of a syringe barrel.The syringe tip or the blunt cannula (which is usually attached to asyringe) is gently pushed through the pre-slit septum to establish fluidcommunication.

I.V. valves, another type of terminal I.V. access device that does notrequire a needle having a sharp tip, are activated by thefrusto-conically shaped tip of a syringe barrel to allow fluidcommunication between the interior of the syringe and the catheter.These valves may contain structure for delivering fluid from a storagecompartment in the valve to the catheter, and are referred to in the artas positive displacement valves. Such a valve is taught in U.S. Pat. No.6,206,861B1. Positive displacement valves were developed to overcome thereflux caused by the disconnection of a syringe tip or cannula from aport or valve. Unfortunately, the positive displacement valves were notdesigned to compensate for the worst-case syringe stopper inducedreflux. When using a traditional syringe assembly containing anelastomeric stopper, the stopper is often compressed when it contactsthe distal end of the syringe barrel at the completion of the flushprocedure. If the user releases the pressure on the plunger after theflush solutions is delivered, the compressed stopper may expand back toits normal size drawing fluid back into the catheter. This fluid isreferred to as syringe stopper induced reflux. Traditional syringeassemblies were designed to accurately deliver medications. Traditionalsyringe assemblies supplied by various suppliers may appear similar butcan vary significantly in terms of performance especially stopperinduced reflux. Because the catheter is inserted into the patient theusers cannot see the reflux when it occurs and therefore cannot takecorrective actions to address a potential problem.

Disconnection induced reflux and syringe stopper induced reflux wouldnot be an issue if all users practice the positive pressure flushingtechniques described hereinabove every time they flushed a VAD. However,user experience, environmental circumstance and patient condition varysignificantly within the hospital setting and even more when oneconsiders other areas that flush procedures are performed such asclinics and home care. As a result, VAD's are frequently occludedresulting in the need for additional professional time, declottingdrugs, removal of catheters and new procedures to place new catheters.All of these interventions come at a cost to the healthcare system andits patients. It is desirable to have syringe assemblies that aredesigned for flush procedures to enhance best clinical practice.Specifically, syringe assemblies that are configured to automaticallyminimize or eliminate reflux without depending entirely on usertechnique. Further, the prior art focuses on syringe assemblies designedto deliver medications and not syringe assemblies that automaticallyprovide additional small amount of flush solution in the I.V. line atthe completion of the flush procedure.

Therefore there is a need for a simple, straight forward, automatic,easy-to-manufacture syringe assembly which helps reduce or eliminatereflux of blood into the catheter during and after the flush procedurehas occurred even if recommended flush procedure techniques are notprecisely followed. For example, prematurely releasing the compressiveforce on the plunger and/or removing the syringe from the I.V. linebefore it is clamped may cause reflux of blood into the catheter, thusincreasing the chance of VAD occlusion.

SUMMARY OF THE INVENTION

The present invention is directed to a syringe assembly for use in flushapplications. The syringe assembly has structure to provide anadditional positive displacement of flush solution after the flushsolution has been substantially delivered from the cavity in the syringebarrel through the application of an additional distally-directed forceprovided by the stopper.

A flush syringe assembly includes a barrel having a cylindrical sidewall with an inside surface defining a chamber for retaining fluid, anopen proximal end and a distal end including a distal wall with a tipextending distally therefrom having a passageway therethrough in fluidcommunication with the chamber. A plunger including an elongate bodyportion having a proximal end, and a distal end is provided. A stopperis slidably positioned in fluid-tight engagement with the inside surfaceof the barrel for driving fluid out of the chamber by movement of thestopper relative to the barrel. The elongate portion of the plungerextends outwardly from the open proximal end of the barrel. The plungerincludes a discontinuity for engaging the barrel for stopping the distalmotion of the plunger before the stopper fully delivers all of theliquid in the chamber. The stopper includes a proximal stopper portionconnected to the distal end of the plunger and a distal stopper portionseparated from the proximal stopper portion by spring means for movingthe distal stopper portion in a distal direction to drive more of theliquid out of the chamber after the discontinuity on the plunger engagesthe barrel to stop the distal motion of the plunger. Spring means may beany spring element which deflects under force and expand when the forceis removed or reduced, such as a coil spring, a pocket of air betweenthe distal and proximal stopper portions, or any element configured toact as a spring such as an annular cantilevered element. The syringeassembly may include a distal stopper portion which is configured toengage the inside surface of the barrel so that less force is requiredto move the distal stopper portion along the chamber than to move theproximal stopper portion along the chamber. This configuration favorsmovement of the distal stopper portion when the spring element expandsbetween the two stopper portions.

The syringe assembly may include a distal stopper portion having atleast one circumferential sealing rib engaging the inside surface of thebarrel and said proximal stopper portion having at least twocircumferential sealing ribs engaging the inside surface of the barrel.

The syringe assembly may be configured so that the discontinuity on theplunger is configured to engage a discontinuity on the barrel to retainthe plunger and prevent further distal and proximal motion of theplunger with respect to the barrel during normal use of the syringeassembly.

The syringe assembly may be configured so that deflection of the springelement desirably occurs when the liquid pressure in the chamber isabout 5 mm Hg (0.1 psi) or more.

When the syringe assembly of the present invention is attached to aperipheral catheter the amount of fluid moving distally in thepassageway after distal motion of the plunger with respect to the barrelhas stopped, is about 0.001 ml or more.

It is also desirable that the desired volume of additional fluid, whenthe syringe assembly is connected to a peripheral catheter, be deliveredin a time of 0.5 second or more. It is preferable that the additionalfluid be delivered in a time of about 2.5 seconds or more.

The syringe assembly may further include structure for allowing airtrapped between the proximal stopper portion and the distal stopperportion to escape toward the open proximal end of the barrel. Thisstructure may include an aperture in the plunger, a less than air-tightfit between the plunger and the proximal stopper portion and/or adiscontinuity in the outside diameter of said proximal stopper portion.

The syringe assembly may further have a needle assembly attachedthereto. The needle assembly includes a cannula having a proximal end, adistal end and a lumen therethrough, and a hub having an open proximalend containing a cavity and a distal end attached to the proximal end ofthe cannula so that the lumen is in fluid communication with the cavity.The needle assembly is removably attached to the tip of the barrel toengagement of the tip to the cavity in the hub so that the lumen is influid communication with the barrel chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the syringe assembly of the presentinvention.

FIG. 2 is an enlarged partially cross-sectioned side-elevation view ofthe syringe assembly of FIG. 1 with a needle assembly attached.

FIG. 3 is an enlarged partial cross-sectional side-elevation view of thesyringe assembly of FIG. 2 shown during the flush procedure.

FIG. 4 is an enlarged partial cross-sectional side-elevation view of thesyringe assembly shown at the completion of the flush solution delivery.

FIG. 5 is an enlarged partially cross-sectional side-elevational view ofthe syringe assembly shown after the completion of flush solutiondelivery and after the stopper has driven an additional amount of flushsolution through the syringe barrel passageway.

FIG. 6 is a side-elevational view illustrating the syringe assembly inuse with a catheter injection site.

FIG. 7 is a side-elevational view illustrating the syringe assembly inuse with another catheter injection site.

FIG. 8 is side-elevational view of an alternative stopper of the presentinvention.

FIG. 9 is a cross-sectional view of the stopper of FIG. 8 taken alongline 9-9.

FIG. 10 is a side-elevational view of another alternative stopper of thepresent invention.

FIG. 11 is a bottom-plan view of the stopper of FIG. 10.

FIG. 12 is a partial side-elevational view of the distal end of analternative plunger of the present invention.

FIG. 13 is an end plan view of the plunger of FIG. 12.

FIG. 14 is a partial, partially-cross-sectioned side-elevation view ofan alternative barrel and plunger of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-7, a syringe assembly 20 according to the presentinvention generally comprises a barrel 21, including a cylindricalsidewall 22 having an inside surface 23 defining a chamber 25 forretaining fluid. The barrel further includes an open proximal end 27 anda distal end 28 having a distal wall 29 with an elongate tip 31extending distally therefrom and having a passageway 32 therethrough influid communication with the chamber. The inside surface of the barrelat the distal wall, indicated as 30, is preferably conically shaped. Thedistal end of the barrel preferably, but not necessarily, includes alocking luer type collar 33 concentrically surrounding tip 31. Thecollar includes an inside surface 34 having at least one thread 35thereon.

A cannula 43 includes a proximal end 44, a distal end 45 and a lumen 46therethrough. The distal end of the cannula may include a sharp tip or ablunt tip 47 as shown. The cannula may be connected directly to the tipof the syringe barrel to establish fluid communication between the lumenand the chamber. Also, the cannula may be part of a needle assembly 42including a hub 49 having an open proximal end 50 containing a cavity 51and a distal end 52 attached to the proximal end of the cannula so thatlumen of the cannula is in fluid communication with the cavity. Thecavity of the hub can be removably frictionally engaged to the tip ofthe barrel.

A plunger 37 includes an elongate body portion 38, a proximal end 39 anda distal end 40. A stopper 41 is disposed at the distal end of theplunger rod through a structure that will be described in more detailhereinafter. The stopper is slidably positioned in fluid-tightengagement with the inside surface of the barrel for drawing fluid intoand driving fluid out of the chamber by movement of the stopper relativeto the barrel. If the syringe assembly is prefilled from themanufacturer, the stopper need not be used for or able to draw fluidinto the barrel. Elongate body portion of the plunger extends outwardlyfrom the open proximal end of the barrel.

Syringe assembly 20 includes a discontinuity on the plunger for engagingthe barrel for stopping the distal motion of the stopper before it fullydelivers all of the liquid from the chamber. In this embodiment thediscontinuity comprises radial projection 57 on the plunger having adistal surface 59 for contacting the barrel to stop the distal motion ofthe plunger before the stopper fully delivers all of the liquid in thechamber. There are numerous structures for limiting the distal motion ofthe plunger with respect to the barrel including any combination ofdiscontinuities such as projections or recesses on the barrel and/or theplunger. For example; a plunger flange 56 can contact finger grips 53 atthe proximal end of the barrel to limit plunger motion. All of thesepossibilities are within the purview of the present invention and theradial projection on the plunger in this embodiment is merelyrepresentative of these many possibilities.

Stopper 41 includes a proximal stopper portion 61 connected to thedistal end of the plunger and the distal stopper portion 62 separatedfrom the proximal stopper portion by spring means for moving the distalstopper portion in a distal direction to drive more of the liquid out ofthe chamber after radial projection 57 engages the barrel to stop thedistal motion of the plunger. In this embodiment, spring means includesa coil spring 63.

In this embodiment, the stopper and the plunger are connected throughthe action of an external thread 58 on the distal end of the plunger andinternal thread 64 in the proximal stopper portion. There are numerousways to connect the stopper and plunger, including a snap-fitarrangement, adhesives, fasteners, ultrasonic welding, two stage moldingand the like. The end of the plunger can engage the exterior of thestopper rather than the interior or just the proximal end of thestopper. All of these various structures for connecting a stopper to aplunger are within the purview of the present invention and the threadedengagement described in this embodiment is merely illustrative of thesemany possibilities. In this embodiment distal surface 63 of the stopperis conically shaped and inside surface 23 of barrel 21 at distal wall 29is also conically shaped.

The stopper may be made of any material suitable for providing sealingcharacteristics while under compression. For example, the stopper may bemade of thermoplastic elastomers, natural rubber, synthetic rubber orthermoplastic materials and combinations thereof. The stopper may beintegrally formed or composed of separate components of the same ordifferent materials joined together. The plunger in this embodiment ispreferably made of material which is more rigid than the stopper such aspolypropylene, polyethylene and the like. Materials should be chosen tobe compatible with the sterilization procedure being used.

In operation, syringe assembly 20 is connected to a needle assembly andfilled with flush solution using known methods. Also, the syringeassembly may be provided pre-filled from the manufacturer or supplier.The flush solution may be any solution intended for flushing ormaintaining the performance of VAD's. It is preferred that the flushsolution be selected from the group consisting of saline flush solutionand heparin lock flush solution. These solutions are known in the artand readily available. An example of a saline flush solution is 0.9%Sodium Chloride USP for injection. An example of a heparin lock flushsolution is 0.9% Sodium Chloride with 100 USP units of Heparin Sodiumper ml or 10 USP units of Heparin Sodium per ml. The syringe with needleassembly attached is used to pierce the pierceable septum or a bluntcannula may be inserted into a pre-split septum of a vial or neck of aglass ampoule containing flush solution and the flush solution is drawninto the syringe barrel by pulling plunger flange 56 in the proximaldirection while holding barrel 21, to draw fluid through the needlecannula into fluid chamber 25.

Alternatively, large quantities of flush syringes may be pre-filled withflush solution during or after the assembly of the syringe using sterilefilling methods. Such prefilled syringes may be supplied with a tip cap,such as tip cap 36 releasably connected to tip 31 sealing passageway 32.It is preferred that the tip cap is formed of material selected from agroup of thermoplastic materials and elastomeric materials such asnatural and synthetic rubber, thermoplastic elastomers or combinationsthereof.

The syringe is now ready for use in flushing a VAD such as a catheter ofan I.V. set. I.V. sets can be very complicated and may include multipleinjection ports, a valve and/or other components. For the purpose ofillustrating the present invention a simplified I.V. set 73 isillustrated in FIG. 6. I.V. set 73 comprises an I.V. site 74 whichincludes a housing 75 having a hollow interior 76 and a septum 77 at itsproximal end. An I.V. line 79 having a conduit therethrough extends fromthe distal end of the housing. I.V. line 79 may be a catheter orconnected to a catheter at its distal end. For this I.V. set, septum 77is pre-slit for use with blunt cannula. The I.V. site may be a valvehaving structure for accepting the syringe barrel tip and beingactivated by the insertion of the tip to establish fluid communicationwith the catheter, such as the valve taught in U.S. Pat. No. 6,171,287.

As previously mentioned, there are two general classifications of VAD's,peripheral catheters and central venous catheters. Peripheral cathetersare used to access veins in the peripheral extremities such as the handand arm. Peripheral catheters are relatively short in length rangingfrom about 14 mm to 48 mm in length, and are available in gauge sizesfrom about 16 to 24. It is believed that the most commonly usedperipheral catheters are 20 gauge having an ID of about 0.81 mm (0.032inch) and 22 gauge having an ID of about 0.66 mm (0.026 inch), andhaving a length of about 25 mm to 32 mm. As used herein, the term“peripheral catheter” is intended to refer to a 20 or 22 gauge catheterhaving a length of about 25 mm. Central venous catheters aresubstantially longer than peripheral catheters and are inserted in thepatient and terminate near the heart.

Blunt tip 47 of cannula 43 may be inserted through pre-split septum 77of I.V. set 73. Alternatively, a sharp tip of a needle cannula may beused to pierce a septum that is not pre-split, or the tip of the barrelmay be engaged with a valve in the IV site. This establishes fluidcommunication between the interior 76 of the I.V. set and the chamber ofthe syringe barrel. The syringe barrel 21 is preferably held via fingergrips 53. Pressure is then applied to flange 56 of the plunger, forexample by a thumb, in the distal direction. This moves plunger 37having stopper 41 on its distal end forcing the liquid such as flushsolution 71 in chamber 25 out of the chamber, through cannula 43 andinto interior 76 of the I.V. set and then through I.V. line 79.

FIG. 3 illustrates syringe assembly 20 during a flush procedure whereinforce F is being applied to flange 56 of the plunger forcing flushsolution 71 from the chamber through passageway 32 and through the lumenof the cannula, through a catheter and into the patient's vein. Itshould be noted that the pressure on the flush solution during the flushprocedure is higher than the patient's blood pressure where the catheterenters the blood vessel, so that fluid moves into the catheter. Thishigher pressure causes distal stopper portion 62 to deflect spring 63and move closer to proximal stopper portion 61 while the plunger isbeing advanced in a distal direction within the barrel. It is desiredthat the spring will deflect under fluid pressure in the barrel of about5 mm Hg. (0.1 psi) or more. It is preferred that the spring will deflectenough during the flush procedure to allow delivery of an additional0.001 ml or more of liquid when the flush procedure is completed. Whenconnected to a peripheral catheter, it is also desirable that the springwill deliver the desired amount of liquid within 0.5 seconds or moreseconds after the completion of the flushing caused by the distal motionof the plunger with respect to the barrel. A spring configured tocompress under fluid pressure of about 5 mm Hg (0.1 psi) or more and toforce about 0.001 ml or more of liquid into a catheter after a flushprocedure, in 0.5 seconds or more is desirable. However, a widevariation in these pressure, displacement and volume parameters can beused to accomplish the desired result. The parameters chosen may dependon the configuration and placement of the VAD, the syringe size and theflush solution being used.

Referring to FIG. 4, the position of the plunger and the stopper at thecompletion of the flush procedure is shown. At the completion of theflush procedure distal motion of the plunger relative to the barrel hasbeen stopped by contact of projection 57 and the barrel. This contact ismade before all of the liquid in the chamber has been delivered. At thispoint, while the user is clamping the I.V. line, distal stopper portion62 is moving back toward its original position with respect to proximalstopper portion 61 by action of spring 63 which has been compressedduring the flush procedure, as illustrated in FIG. 5, and in doing so isforcing additional I.V. solution out of the chamber and through thepassageway of the barrel.

The positive displacement of fluid in the passageway in a distaldirection will help prevent reflux while the I.V. line is being clampedand the syringe is being removed. After the I.V. line is clamped, thesyringe assembly may be removed from the I.V. set. It should be notedthat removing a syringe from an I.V. set can promote reflux by thewithdrawal of solid elements of the syringe and/or cannula from a closedsystem. This potential withdrawal reflux can be compensated for by thepositive displacement of flush solution by the stopper in the syringeassembly of the present invention.

FIG. 7 shows an alternative simplified I.V. set to illustrate a flushprocedure without a needle assembly. In FIG. 7, I.V. set 173 comprisesan I.V. site 174 which includes a housing 175 having a hollow interior176 and a luer fitting 178 at its proximal end. An I.V. line 179 havinga conduit therethrough extends from the distal end of the housing. TheI.V. line may be a catheter or connected to a catheter at its distalend. The I.V. set illustrated in FIG. 7 is simplified to demonstrate theinvention. In most cases a luer fitting such as luer fitting 178 wouldbe part of a one-way valve in the I.V. set. The elongate tip of thebarrel is inserted and engaged with the luer fitting to establish fluidcommunication between interior 176 of the I.V. set and the chamber ofthe syringe barrel. Pressure is then applied to a flange on the proximalend of the plunger, for example by a thumb, in the distal direction.This moves plunger 37 having stopper 41 on its distal end, forcingliquid such as flush solution 71 in chamber 25 out of the chamber,through passageway 32 in the elongate tip into hollow interior 176 ofthe I.V. set and then through I.V. line 179. The remainder of the flushprocedure is substantially identical to the procedures described whenusing I.V. set 73 of FIG. 6. One way to clamp an I.V. line is throughthe use of locking member 85 which is a thin element usually made ofplastic having a slot 86 therein. The slot has an enlarged portion 87which allows flow through the I.V. line and a narrow portion 88. At thecompletion of the flush procedure the I.V. line is forced into thenarrow portion of the slot which compresses the I.V. line to a closedconfiguration. Based on the experience of the person performing theflush procedure and the clinical circumstances at the time of theprocedure, e.g. the patient is in an agitated state, it may be difficultto clamp the line with one hand while holding the syringe with the otherhand. The present invention can allow the user to momentarily releasethe syringe and use two hands to clamp the I.V. line because of thesyringe is still exerting a positive pressure on the flush solution asthe distal wall of the stopper moves back toward its original shape.

Another feature of the present invention is that the distal stopperportion may be configured to engage the inside surface of the barrel sothat less force is required to move the distal stopper portion along thechamber than the force required to move the proximal stopper portion.There are many ways to accomplish this result including having moreannular ribs on the proximal stopper portion than on the distal stopperportion or having a larger diameter proximal stopper portion to increasethe friction between the barrel and the proximal stopper portion. Alsodifferent materials, having different coefficients of friction ordifferent surface configurations may be used to make the distal stopperportion move more easily in the barrel than proximal stopper portion.This feature is preferred because it can allow the user to momentarilyrelease the distally-directed pressure on the plunger at the completionof the flush procedure since expanding spring will tend to move thedistal stopper portion forward rather than moving the proximal stopperportion in a rearward or proximal direction. In the present embodimentdistal stopper portion 62 has one annular sealing rib 65 and proximalstopper portion 61 has two (2) annular sealing ribs 67.

FIGS. 8 and 9 illustrate an alternative embodiment of the stopper of thepresent invention. In this embodiment stopper 141 includes proximalstopper portion 161 having an annular sealing rib 167 and an internalthread 164 for engaging a plunger. A distal stopper portion 162 havingan annular sealing rib 165 is separated from the proximal stopperportion by spring element 163 provided for moving the distal stopperportion in a distal direction to drive liquid out of the chamber of asyringe barrel after the proximal stopper portion stops moving in thedistal direction. The stopper in this embodiment functions similarly tothe stopper in the embodiment of FIGS. 1-7. Spring element 163 is acantilevered annular element comprising an outwardly divergingfrusto-conically shaped portion 168 and an inwardly convergingfrusto-conically shaped portion 169. The fluid pressure in the chamberwill deflect the annular cantilevered element during a flush procedureand afterward the energy in the annular cantilevered element will urgethe distal stopper portion to its original position with respect to theproximal stopper portion.

FIGS. 10 and 11 illustrate another alternative stopper of the presentinvention. In this embodiment stopper 241 includes a proximal stopperportion 261 having annular sealing ribs 267 and a distal stopper portion262 separated from the proximal stopper portion by spring elements 263.Stopper 241 functions similarly to the stopper of the embodiments ofFIGS. 1-7. In addition stopper 241 includes one or more axial grooves270 cutting through annular sealing ribs 267. In order to more carefullycontrol the forces from which spring element 263 compresses and expands,it may be desirable to remove trapped air between the distal stopperportion and the proximal stopper portion. Since the air would also actas a spring element. With the air vented toward the open proximal end ofthe barrel, the primary determiner of the spring element force will bethe spring element itself and the frictional relationship between thestopper portions and the inside of the barrel. It should also be notedthat without a means of allowing air trapped between the proximalportion and the distal portion of the stopper to escape toward the openproximal end of the barrel, the air alone, without a mechanical springcan comprise a spring element. Air trapped between the proximal stopperportion and the distal stopper portion can also be allowed to escape byhaving a less than air-tight fit between the plunger and the proximalstopper portion and/or by having an aperture in the distal end of theplunger.

FIGS. 12 and 13 illustrate an alternative plunger of the presentinvention. In this embodiment, plunger 337 includes an elongate bodyportion 338 having a distal end 340 with aperture 360 therethrough.Aperture 360 allows air trapped between the distal stopper portion andthe proximal stopper portion, in some embodiments, to escape into thechamber and out of the open proximal end of the barrel.

FIG. 14 illustrates an alternative barrel and plunger of the presentinvention. In this embodiment a barrel 421 includes a cylindrical sidewall 422, an open proximal end 427 and finger grips 453 on the proximalend. The barrel also includes an inwardly directed annular projection454. Plunger 437 includes an elongate body portion 438 having a proximalend 440 including a proximal flange 456 and a radial projection 457.

In use, radial projection 457 on the plunger engages the barrel forstopping distal motion of the plunger before the stopper fully deliversall of the liquid from the chamber. In addition, in this embodiment,secondary radially directed projection 455 on the plunger will snap pastannular projection 454 at the completion of the flush procedure. Theinteraction of radial projections 455 and 457 on the plunger and annularprojection 454 in the barrel act to retain the plunger and preventfurther distal and proximal motion of the plunger with respect to thebarrel during normal use of the syringe assembly. There are manycombinations of discontinuities on the plunger and/or the barrel forretaining the plunger to prevent further distal and proximal motion, andthe structure of the embodiment of FIG. 14 is merely representative ofthese many possibilities.

What is claimed is:
 1. A flush syringe assembly for reducing reflux ofblood into a vascular access device during and after a flush procedurecomprising: a barrel including a cylindrical side wall having an insidesurface defining a chamber for retaining fluid, an open proximal endhaving an inwardly directed annular projection and a distal endincluding a distal wall with a tip extending distally therefrom having apassageway therethrough in fluid communication with said chamber; aplunger including an elongate body portion having a proximal end havinga radially directed projection and a secondary radially directedprojection, and a distal end, a stopper slidably positioned influid-tight engagement with said inside surface of said barrel fordriving fluid out of said chamber by movement of said stopper relativeto said barrel, said elongate body portion extending outwardly from saidopen proximal end of said barrel, the radially directed projection onthe proximal end of the plunger and the secondary radially directedprojection positioned to snap past the inwardly directed annularprojection on the proximal end of the barrel to retain the plunger andto prevent further distal and proximal motion of the plunger withrespect to the barrel; a discontinuity including an outwardly directedfixed radial projection on said elongate body portion on said plungerhaving a distal surface extending beyond the cylindrical side wall ofthe barrel for direct engagement of the plunger with said barrel forstopping the distal motion of said plunger before said stopper fullydelivers all liquid from said chamber, said stopper including a proximalstopper portion connected to said distal end of said plunger and adistal stopper portion separated from said proximal stopper portion by aspring for moving said distal stopper portion in a distal direction todrive more liquid out of said chamber after said discontinuity on saidplunger engages said barrel to stop distal motion of said plunger,wherein said distal stopper portion has at least one circumferential ribengaging said inside surface of said barrel and said proximal stopperportion has at least two circumferential ribs engaging said insidesurface of said barrel to engage said inside surface of said barrel sothat less force is required to move the distal stopper portion alongsaid chamber than said proximal stopper portion.
 2. The syringe assemblyof claim 1 wherein said spring element includes a coil spring.
 3. Thesyringe assembly of claim 1 wherein said spring is an annularcantilevered element.
 4. The syringe assembly of claim 1 wherein saidspring includes an air space between said distal stopper portion andsaid proximal stopper portion.
 5. The syringe assembly of claim 1wherein said discontinuity on said plunger is configured to engage adiscontinuity on said barrel to retain the plunger and prevent furtherdistal and proximal motion of said plunger with respect to said barrelduring normal use of said syringe assembly.
 6. The syringe assembly ofclaim 1 wherein said plunger defines an aperture for allowing airtrapped between said proximal stopper portion and said distal stopperportion to escape toward said open proximal end of said barrel.
 7. Thesyringe assembly of claim 1 wherein there is a less than air-tight fitbetween said plunger and said proximal stopper portion for allowing airtrapped between said proximal stopper portion and said distal portion toescape toward said open proximal end of said barrel.
 8. The syringeassembly of claim 1 wherein an outside diameter of said proximal stopperportion includes at least one discontinuity for allowing air trappedbetween said proximal stopper portion and said distal portion to escapetoward said open proximal end of said barrel.
 9. The syringe assembly ofclaim 1 wherein deflection of said spring occurs when said liquidpressure is about 5 mm Hg. (0.1 psi) or more.
 10. The syringe assemblyof claim 1 including flush solution in said chamber.
 11. The syringeassembly of claim 10 wherein said flush solution is selected from thegroup consisting of saline flush solution and heparin lock flushsolution.
 12. The syringe assembly of claim 10 further including a tipcap releasably connected to said tip of said syringe barrel for sealingsaid passageway.
 13. The syringe assembly of claim 1 wherein saidstopper is made of material selected from the list consisting ofthermoplastic elastomers, natural rubber, synthetic rubber,thermoplastic materials and combinations thereof.
 14. The syringeassembly of claim 1 further comprising a needle assembly including acannula having a proximal end, a distal end and a lumen therethrough,and a hub having an open proximal end containing a cavity and a distalend attached to said proximal end of said cannula so that said lumen isin fluid communication with said cavity, said needle assembly beingremovably attached to said tip of said barrel through engagement of saidtip to said cavity so that said lumen is in fluid communication withsaid chamber.
 15. The syringe assembly of claim 1, wherein a single usercan engage the discontinuity with the barrel to prevent distal motion ofthe plunger using one or two hands.